Air Conditioning Terms
An appliance, system, or mechanism designed to dehumidify and extract heat from an area. Usually, this term is reserved for smaller self-contained units such as a residential system.
British Thermal Unit (BTU)
Any of several units of energy (heat) in the HVAC industry, each slightly more than 1 kJ. One BTU is the energy required to raise one pound of water one degree Fahrenheit, but the many different types of BTU are based on different interpretations of this “definition”. In the United States, the power of HVAC systems (the rate of cooling and dehumidifying or heating) is sometimes expressed in BTU/hour instead of watts. Abbreviated BTU or Btu.
A component in the basic refrigeration cycle. Contains a compressor that adds heat to refrigerant, then with the assistance of a fan condenses that compressed gas to a liquid.
A digital or mechanical device that controls the operation of a system. It may simply turn a device on and off, or it may more subtly modulate the set point of components. Most controllers are automatic but have user input such as temperature set points.
Gas Furnace Heat Exchanger
A cover of a duct opening, often rectangular, containing multiple parallel slots through which air may be delivered or withdrawn from a ventilated space. The grille directs the airflow in a particular direction and prevents the passage of large items.
A heating coil is the part of the system that converts electricity to heat. Electricity is running through a specially designed wire that glows hot and the air is then blown over it producing warm air.
A heat pump is very similar to a condenser; however, when there is a call for heat it reverses the refrigerant flow and produces a hot indoor coil rather than a cold.
A split system is the combination of an outdoor unit and an indoor unit. This is the most common type of system.
The condition where liquid refrigerant is colder than the minimum temperature required to keep it from boiling would change it from a liquid to a gas phase. Subcooling is the difference between its saturation temperature and the actual liquid refrigerant temperature.
General term is used to refer to the set or a subset of components that perform a specific HVAC function within a building.
A thermostat is a system that monitors and regulates a heating or cooling system. It can be used to set the desired temperature at which it keeps the environment either heated or cooled.
Two-Stage (cooling and heating)
A two-stage air conditioner is designed to operate on high and low settings during different weather conditions and seasons. The high setting is used during extreme weather, and the low setting is used during moderate weather. This type of air conditioner produces a balanced temperature and is in use for a longer period of time.
TXV – Thermostatic Expansion Valve
A thermostatic expansion valve is a piece of equipment that meters the flow of liquid refrigerant into the evaporator while measuring the vapor refrigerant leaving the evaporator. It thereby controls the superheating at the outlet of the evaporator.
Variable Air Volume
An HVAC system that has a stable supply-air temperature, and varies the airflow rate to meet the temperature requirements. Compared to constant air volume systems, these systems conserve energy through lower fan speeds during times of lower temperature control demand. Most new commercial buildings have VAV systems. VAVs may be bypass type or pressure dependent. Pressure dependent type VAVs save energy while both types help in maintaining temperature of the zone that it feeds. Abbreviated VAV.
A zoning system sections a building or a space into zones, which are controlled independently of each other. This is beneficial when different areas or rooms of a building have different temperatures as well as when the desired temperatures in different rooms are different. Temperature is controlled by different thermostats.